Measuring the walking or running speed of a person is of importance for science, therapy and training. Information obtained by such a measurement can be used to improve human performance, for example in sports and rehabilitation.
A number of technologies exist that allow measurement of running speed, these include the use of GPS (global position system), accelerometer inertia devices, accelerometer based pedometers and timing/counting sensors. Each of these methods has varying degrees of accuracy and each has its limitations. General timing and counting devices do not offer a very reliable measurement of speed or distance since they rely upon the assumption that the stride length of a person remains constant irrespective of speed and environment. From the location as determined by GPS the speed can be derived in a straightforward way by measuring the elapsed time. However, GPS based speed measurement requires that the sensor is always in view of a number of satellites. Therefore it is often not possible to measure the speed in high rise urban areas, heavily wooded or mountainous areas, inside buildings like indoor sport buildings or in tunnels and subways.
For training and therapy one is often not only interested in speed but also in other parameters characterising the walking or running behaviour of the person. Typically one may be interested in biomechanical parameters like foot strike location, speed of pronation, contact time, and heel off speed. These parameters cannot be obtained with a GPS system because GPS only provides information about the location of the person. So, to obtain the biomechanical parameters additional sensors have to be used. Such additional sensors make the system expensive and complex.
U.S. Pat. No. 6,360,597 discloses a system for determining the gait line of a walking person. A gait line is a line that illustrates how the average pressure, or better the centre of pressure, of a foot changes during the time that the foot is in contact with the ground. This known system comprises force-sensing sensors that are inserted into a shoe. The spatially averaged output signal of the sensors provides a gait line in a two dimensional space. In addition, this patent publication discloses a method to distinguish different phases of the foot contact with the floor. In particular this known method allows determining the duration of heel strike, toe-off, and mid-stance. So, this known method provides a limited number of basic parameters concerning the contact time of the different parts of a foot with the floor.
U.S. Pat. No. 4,578,769 discloses a method for determining the speed of a person while running. This known method comprises the use of a sensor that is located in the sole of a shoe for determining whether or not the foot is in contact with the ground. The time during which the foot is in contact with the ground is used to determine the running speed of the person. For each particular runner a linear relationship between the contact time and the running speed, which relationship is different for each person, is determined empirically. This relationship is stored in a microprocessor and is used to calculate the running speed.
However, contact time depends on factors other than running speed alone. Therefore this approach has a limited accuracy.
US patent application 2002/0040601 discloses a motion analysis system comprising accelerometers and a tilt sensor that are mounted on a shoe. The average horizontal speed of the shoe as determined from the accelerations measurements and analysis corresponds to the speed of the person. In addition also parameters like the stride length, the height of the foot off the ground, and the degree of pronation can be derived from the measurements.
A problem that one encounters when using accelerometers for deriving the walking or running speed from the foot motion of a person is that this method can become less accurate if the accelerometers are mounted incorrectly or if they become disorientated during use. If the foot is swung through in an unusual orientation the accuracy of the model can be additionally compromised. Unusual dynamic movements during the foot swing can also disrupt the measurement. Another problem of a method using an accelerometer is that additional sensors of another type have to be applied to derive parameters which require information about the gait line.